The present invention relates to a joint for a truss structure, more particularly such a joint for removably attaching a ball member to an end of a bar member to form a truss structure.
It is known to submerge truss structures under water to form an artificial habitat for fish, or for minimizing the erosion effect of waves on the undersea terrain. Truss structures are typically made by joining a plurality of bar members together by means of concrete balls. The bar member may comprise a concrete cylinder through which a tension member, such as a tension cable, extends. The ends of the tension cable may be attached to the concrete balls at opposite ends of the bar member so that tensile forces exerted on the bar member are borne by the tension cable, while compression forces exerted thereon are borne by the concrete cylinder.
The conventional truss structure elements are difficult to assemble, since the ends of the tension member extending through the bar must be attached to the ball member. This is usually accomplished by a press fitting connection between projection members fixed on the end of the tension member which must be inserted into holes on the ball member.
Another disadvantage of the known truss joints is their poor assembly accuracy caused by the inability of the connecting mechanisms to facilitate adjusting the length of the tension member.
Additional disadvantages involve the fabrication of the concrete ball member. Since the concrete ball used in conventional truss structures is made in a hollow spherical shape to compensate for the difference in specific weights between concrete and sea water, it must be formed around a spherical core. This spherical core is extremely difficult to remove from the concrete ball member.
As is well known in the art, concrete is strong against compression forces, but is weak against tensile forces. Therefore, a concrete ball member cannot bear large tensile forces. Thus, it is quite desirable to provide a ball member having simplified construction, while at the same time increasing its strength against tensile forces.